The present invention relates to the improved placement and self-alignment of structures associated with an integrated circuit and, more particularly, to structures, including mechanical and electrical connection structures, designed to self-align into their as-designed orientation during the solder-reflow phase of their assembly.
In the packaging of integrated circuits, the “chip” or die is typically attached to the die “paddle” or “pad” portion of a leadframe structure by a die-attach material, typically a solder paste created as a mixture of solder particles and a flux-containing gel. During the assembly process, the solder paste acts as a temporary adhesive that holds the die to the leadframe while the parts are heated during a subsequent solder reflow process step in which the solder paste is thermally liquefied and thereafter solidified to secure the die and leadframe together.
The die includes contact pads that are electrically connected to respective leads or contact areas on the leadframe by thin bonding-wires using ball bond (i.e., “nail-head”) or wedge bond formations and thermocompressive or thermosonic bonding techniques.
In some applications involving higher than usual currents, a plurality of bonding wires can be used to connect various conductive pads on the die to leads, pads, or areas on the leadframe to accommodate the current involved. As the current levels increase, the number of bonding wire connections increases to the point where the use of a sufficient plurality of bonding wires to carry the current load becomes impracticable. Rather than use a multitude of bonding wires in high-current applications, such as those involving power-switching or power-handling transistors, connections can be made from the die to the leadframe via a conductive ribbon or pre-formed clips fabricated from copper or a copper alloy, for example, as the conductive material.
In those cases where a pre-formed clip is used, the clip is typically placed on the die/leadframe assembly by a robotic ‘pick-and-place’ machine and maintained in position by a quantity of solder paste. As occasionally happens, the clip is mis-aligned during placement; in some cases the mis-aligned clip can contribute to product reliability issues. Additionally, parts and structures undergoing solder reflow have been know to “swim” or “move around” on the liquefied solder as a consequence of differential heating rates and to thereby lose their as-placed alignment.